Mathematica is FANATIC about correct spelling and capitalization and [] versus () versus {} and := versus = versus == and there is even an === and those are all completely different. Make any tiny error in any one of those and you will get incorrect results or strange messages you don't know how to interpret or just what you typed in given back to you or sometimes crashes or even nothing at all. Many things in Mathematica are similar but different from the usual blackboard and textbook notation. Watch out for that.

It is possible that someday there might be a "novice mode" that will try to recognize all the little misunderstandings that new users fall into again and again. Hopefully that will turn the questionable item into bright red blinking text with a little bouncing finger pointing to that and a little bubble next to it saying "ummm... did you perhaps want this instead of that?!?!" Unfortunately we don't have that yet, but Mathematica is only 25 years old and there is still hope.